1. The Field of the Invention
The present invention is in the field of customized dental trays used to provide a desired dental treatment to a person's teeth. More particularly, the invention relates to customized dental trays that are formed using either a person's teeth or a stone model of the person's teeth as a template. The tray can be used for dental treatments such as bleaching, administration of fluoride, or application of other medicines.
2. The Relevant Technology
Virtually all people desire white or whiter teeth. To achieve this goal, people either have veneers placed over their teeth or have their teeth chemically bleached. In the past, patients who desired to have their teeth bleached had to submit to conventional in-office bleaching techniques. The process generally involves: (1) making an alginate impression of the patient's teeth; (2) making a stone cast or model of the impression; (3) vacuum forming a dental tray from the model, usually from a sheet of thin ethyl vinyl acetate (EVA) material, and trimming to exclude gingival coverage. This method results in a tray that is soft and flexible, that is very accurately customized to the patient's teeth, but the method is time consuming and the resulting tray is expensive.
Because of the high cost of these very accurate custom trays, less costly alternatives have been developed, but these alternatives have substantial disadvantages in terms of accuracy and comfort of the finished formed tray.
One alternative is the so-called “boil and bite” tray. A relatively thick, non-custom preformed tray (similar to a mouth guard) made of EVA or polyethylene or other material is submerged in boiling water. Upon removal from the water, the tray is quickly placed inside the patient's mouth. The patient quickly applies contact pressure to make an impression of the biting surfaces of the user's teeth. One problem with “boil and bite” trays is that they are relatively thick and bulky, which make them intrusive and uncomfortable to wear. The thickness of large, bulky perform trays also limits the accuracy with which they can conform to the user's teeth and/or gums.
To the extent that preform trays made from EVA and like materials are made with thinner walls, such trays are extremely difficult to work with because they tend to shrivel and collapse outside extremely narrow windows of temperature and heating time. For example, if left in a hot water bath too long (i.e., for more than a few seconds) they can quickly become limp and lose their pre-form shape, making it difficult or impossible to make an impression of the user's teeth. In view of the foregoing, “boil and bite” trays that do not have the tendency to collapse and shrivel when heated generally do not accurately conform to the user's teeth and are bulky and uncomfortable to wear.
Another alternative for teeth bleaching involves non-customized strips of a flexible plastic material coated with a bleaching agent that can be applied to the teeth. Such strips are placed against the teeth by the user to cover the teeth. Because such strips are flimsy and limp at room temperature (i.e., are not resilient or rigid), they are not useful for creating a customized dental tray.
Another alternative is a dual tray assembly as disclosed in U.S. Pat. No. 5,616,027 to Jacobs et al. The dual tray assembly is composed of an outer tray that supports or carries an inner tray made of a thermoplastic material comprising EVA. In use, the tray assembly is submerged in hot water, where the inner tray becomes pliable and moldable and the outer tray remains rigid. “Because of the material and the thinness of the walls of the inner tray, the inner tray will substantially lose integrity of its shape and form during the heating process . . . .” (Col. 4, ll. 14–16.) Thus, “[t]he carrier tray is necessary during the heating, handling and forming process.” (Col. 4, ll. 16–17.) The heated assembly is then placed in the mouth of the patient where the inner tray takes an impression of the person's teeth. The generally thinner inner tray results in a final tray that is much thinner and more comfortable to wear compared to conventional “boil and bite” trays that are sufficiently thick that they do not need a supporting carrier tray. Nevertheless, the outer tray can inhibit accurate conformation of the inner tray to the shape of the patient's teeth.
Another problem with EVA are concerns about its toxicity. Whereas trays made using EVA are generally safe to use, the FDA has guidelines that strictly controls how EVA can be used. Notwithstanding the foregoing deficiencies, EVA finds wide use in the manufacture of dental trays, which is strong evidence of the inadequacy of other possible plastic materials that are suggested in various existing patents relating to tray technology. EVA is generally preferred due to its softness and flexibility and the ease in which it can be heated and formed into a dental tray compared to other plastic materials suggested in the art.
In view of the foregoing, there is an ongoing need to develop new materials for use in manufacturing preformed trays and sheets that can be easily formed into customized trays that are thin-walled, flexible, comfortable, and that accurately reflect the shape of the person's teeth.